When operated properly, incinerators can achieve high efficiency in destroying hazardous organic materials in treating both hazardous wastes and mixed wastes. However, problems arise during improper operations or upset conditions, when dioxanes, furans, and other toxic materials may be released at dangerous levels. By means of careful design and operation, which are regulated by the Environmental Protection Agency, and various state and local agencies, dangerous emission levels can be avoided.
Fluid bed incineration for hazardous organic waste is an old concept and has been practiced for years by several companies, one of which being the Doff-Oliver Company. In the June 1992 edition of "Chemical Engineering Progress", John F. Mullin of the Dorr-Oliver Company reviewed the waste incinerator designs used to treat hazardous waste over the past fifteen years. Examples of the Dorr-Oliver technology are included in the Fitch et al. U.S. Pat. No. 4,159,682 issued Jul. 3, 1979 showing separate dryer and incinerator fluid beds wherein the dryer off gases are handled separately from the incinerator off gases and hot bed material from the incinerator is used to heat the moist feed material to the dryer. However, the Fitch et al. '682 patent vents incinerator off gases to the atmosphere. Another Dorr-Oliver patent is the Fitch et al. U.S. Pat. No. 4,232,614 issued Nov. 11, 1980, which also teaches separate air dryer and incinerator mechanisms, both of which have off gas streams which are treated separately but which eventually exit the system to the atmosphere.
Another company that has been active in the incineration of hazardous waste material was the Envirotech Corporation of Menlo Park, Calif., later bought by the Lurgi Company However, in the 70's and early 80's, the Envirotech Company operated a number of systems in an attempt to treat sewage sludge and industrial waste. Representative systems include rotary kiln systems and multiple hearth systems which were used to classify and dry sludge and thereafter incinerate same, for instance see the Isheim U.S. Pat. No. 4,153,411, the Isheim U.S. Pat. No. 4,248,164, the Lombana U.S. Pat. No. 4,215,637. There are other patents issued to Envirotech which are also pertinent; however, none of these patents relate to systems in which no vapor emissions exit to the atmosphere.
Briefly, other companies through the years, have used fluidized bed systems which treat hazardous organic compounds inherent in the operation of the system. For instance, the Foster-Wheeler Energy Corporation developed significant technology relating to the fluidized bed treatment of coal as for instance in the Daman U.S. Pat. No. 4,275,668 issued Jun. 30, 1981, the Taylor U.S. Pat. No. 4,197,086 issued Apr. 8, 1980 and other Foster-Wheeler patents of this general time frame; however, none of the Foster-Wheeler systems and processes to the knowledge of the applicants included systems which are unvented to the atmosphere. Combustion Power Company in Palo Alto, Calif. investigated fluidized bed separation and incineration, see the Smith et al. U.S. Pat. No. 3,654,705 issued Apr. 11, 1972. A large waste incinerator was operated in Palo Alto in the 1970's and this may have been a precursor to such system. Other representative technologies in the hazardous waste disposal business include rotary kilns useful for incineration and such processes were routinely practiced throughout the United States in the 70's and 80's for incinerating waste including hazardous waste of both solid and liquid, but all of these incineration technologies involve venting off gases to the atmosphere.
Finally, there is a rotary kiln process which has been successfully used to remediate PCBs at Waukegan Harbor, Ill. and at Wide Beach, N.Y., which produces a reduced amount of off gases from the remediation, represented by the Taciuk U.S. Pat. Nos. 4,180,455, 4,280,879, 4,285,773 and 4,306,961. However, the Taciuk patents still produces significant quantities of vapor which has to be treated by down stream equipment. Various technologies presently exist which combine incineration with chemical reaction in treating hazardous materials and representative examples of these are the Eggers, III U.S. Pat. No. 3,932,118 issued Jan. 13, 1976 and U.S. Pat. No. 4,040,865 issued Aug. 9, 1977, both of which relate to the pyrolysis of PCB material combined with incineration in a fluidized bed wherein CaCO.sub.3 particles are used to react with chlorine produced during the destruction of PCB to produce CaCl.sub.2. Nevertheless, none of the technologies recited above, although representative of the presently known treatment of hazardous waste materials by fluidized beds, multiple hearth furnaces and rotary kilns, illustrate a process in which no off gases from the treatment of the hazardous waste material per se are emitted to the atmosphere.
The above quoted technologies while effective to remediate hazardous waste fall short because satisfying the local public on all aspects concerning the operations of an incinerator is often more difficult than demonstrating to the scientific community and the appropriate agencies that the emission standards can be met. The public's main concern with incinerators is the risk of toxic organic emissions or radioactive emissions. The public perceives nearby incinerators to be a risk to health imposed by the government or industry, and also a factor tending to lower property values. As a result, the siting of incinerators has become very contentious and expensive. A process that does not produce emissions, such as the inventive process described herein, may meet with greater public acceptance.
Work has been done previously to reduce or eliminate the emissions from incinerators. Stull and Golden at EG&G Rocky Flats have evaluated off-gas capture systems from a fluidized-bed oxidation unit. In the two systems evaluated, 85% of the off-gas from the fluidized bed oxidizer would be recycled with oxygen make-up, and the remaining 15% would be compressed to liquid CO.sub.2, stored in tanks, sampled, and ultimately released. One process requires compression to 75 bar (1100 psia) at 16.degree. C. (60.degree. F.), and the other requires compression to 24 bar (350 psia) at -26.degree. C. (-15.degree. F.). Another approach was taken by Camp and Upadhye of Lawrence Livermore National Laboratory. In their proposed process, the mixed waste could be destroyed in any one of many types of incinerators with an oxidant of oxygen and recycled CO.sub.2. The off-gases would be directly quenched with water in a venturi scrubber. Acid gases would be removed by reacting with sodium hydroxide in a packed tower, and CO.sub.2 would be removed in a second packed tower by contacting with calcium hydroxide. The remaining oxygen, CO.sub.2, water vapor, and trace gases would be recycled to the waste destructor with makeup oxygen. The solid materials in the slurries exiting the packed towers would be consolidated to moist solids, which could be buried. The Livermore process would produce a large amount of solids for burial, which was viewed by them as a disadvantage.
Still another approach is set forth in the recently issued U.S. Pat. No. 5,179,903 issued Jan. 19, 1993, to Abboud et al., which uses enriched air and high incineration temperature along with several scrubbers to treat effluents from the system.
The inventive process is designed for treating mixed wastes that have accumulated at Argonne National Laboratory (ANL) over several decades. The type of mixed waste stored an ANL that has the largest volume is scintillating counting waste, which is stored in 200 drums of 55-gal. capacity. Each drum holds 2000-4000 vials of toluene-based scintillation fluid containing radioactive materials from a wide range of projects. The vials are packed in vermiculite, which also must be treated as a mixed waste. With the proper head-end step to separate the organic liquid from the balance of the materials, this waste inventory could be treated by the inventive process hereinafter described. Also, the biological mixed waste at ANL could be treated by the proposed process, which would destroy the biological materials and separate the inorganic low-level radioactive waste for burial.
The treatment of these wastes at the ANL site is a difficult problem because ANL is located near suburban residences. Installation of a conventional incinerator would be out of the question. The inventive process and system does not release gases from the equipment during the thermal destruction of organic materials. The only products from the inventive system and process are liquid water and calcium carbonate. In one version of the invention, treating the limited quantities of ANL waste, the calcium carbonate and water produced would be mixed with cement-making materials to produce cement. This solid material would be the only product from the process.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.